U.S. patent application number 16/695837 was filed with the patent office on 2020-06-04 for method for identifying a correct operation of an electrical switching unit, computer program product for executing such a method.
The applicant listed for this patent is Conti Temic Microelectronic GmbH. Invention is credited to Erwin Kessler.
Application Number | 20200177177 16/695837 |
Document ID | / |
Family ID | 69781272 |
Filed Date | 2020-06-04 |
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United States Patent
Application |
20200177177 |
Kind Code |
A1 |
Kessler; Erwin |
June 4, 2020 |
METHOD FOR IDENTIFYING A CORRECT OPERATION OF AN ELECTRICAL
SWITCHING UNIT, COMPUTER PROGRAM PRODUCT FOR EXECUTING SUCH A
METHOD, AND FULL BRIDGE CIRCUIT WITH A CONTROL DEVICE FOR EXECUTING
SUCH A METHOD
Abstract
A method for identifying correct operation of an electrical
switching unit, having a full bridge circuit and inductive load
operated by the full bridge circuit. The full bridge circuit
includes a first semiconductor switching element supplying the
inductive load with a first supply voltage potential and a second
semiconductor switching element supplying the inductive load with a
second supply voltage potential, having a smaller value than the
first supply voltage potential. The first and second semiconductor
switching element each have a diode. The method determines that the
first semiconductor switching element changes from an activated
state into a deactivated state, measures a voltage applied to the
second semiconductor switching element, compares the measured
voltage with a first threshold and detecting that, if the measured
voltage on the second semiconductor switching element falls below
the second supply voltage potential by the predefined first
threshold, the electrical switching unit is operating
correctly.
Inventors: |
Kessler; Erwin; (Bad
Saulgau, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Conti Temic Microelectronic GmbH |
Numberg |
|
DE |
|
|
Family ID: |
69781272 |
Appl. No.: |
16/695837 |
Filed: |
November 26, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H03K 17/18 20130101;
G01R 31/327 20130101; H03K 17/0822 20130101; H03K 17/30
20130101 |
International
Class: |
H03K 17/18 20060101
H03K017/18; H03K 17/30 20060101 H03K017/30 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 3, 2018 |
DE |
10 2018 220 861.1 |
Claims
1. A method for identifying a correct operation of an electrical
switching unit, which has a full bridge circuit and an inductive
load operated by the full bridge circuit, the full bridge circuit
comprising a first semiconductor switching element to supply the
inductive load with a first supply voltage potential and a second
semiconductor switching element to supply the inductive load with a
second supply voltage potential which has a lower value than the
first supply voltage potential, wherein the first semiconductor
switching element and the second semiconductor switching element
each have a diode and wherein the method comprises: determining
that the first semiconductor switching element changes from an
activated state into a deactivated state, measuring a voltage
applied to the second semiconductor switching element, comparing
the measured voltage with a predefined first threshold value and
identifying that, if the measured voltage on the second
semiconductor switching element falls below the second supply
voltage potential by the predefined first threshold value, the
electrical switching unit is operating correctly.
2. The method as claimed in claim 1, wherein the step of
identifying the correct operation of the electrical switching unit
also comprises: determining a first time at which the first
semiconductor switching element changes from the activated state
into the deactivated state, determining a second time at which the
voltage measured on the second semiconductor switching element
falls below the second supply voltage potential by the first
threshold value, and identifying the correct operation of the
electrical switching unit if the second time occurs within a
predetermined duration after the first time.
3. The method as claimed in claim 1, wherein the correct operation
of the electrical switching unit is only identified if the voltage
measured on the second semiconductor switching element falls below
the second supply voltage potential by the first threshold value
for a pre-defined first minimum duration.
4. The method as claimed in claim 1, further comprising: allowing a
re-activation of the first semiconductor switching element if the
correct operation of the electrical switching unit has been
identified.
5. A method for identifying a correct operation of an electrical
switching unit, which has a full bridge circuit and an inductive
load operated by the full bridge circuit, the full bridge circuit
comprising a first semiconductor switching element to supply the
inductive load with a first supply voltage potential and a second
semiconductor switching element to supply the inductive load with a
second supply voltage potential which has a lower value than the
first supply voltage potential, wherein the first semiconductor
switching element and the second semiconductor switching element
each have a diode and wherein the method comprises: determining
that the second semiconductor switching element changes from an
activated state into a deactivated state, measuring a voltage
applied to the first semiconductor switching element, comparing the
measured voltage with a predefined second threshold value and
identifying that, if the measured voltage on the first
semiconductor switching element falls below the first supply
voltage potential by the predefined second threshold value, the
electrical switching unit is operating correctly.
6. The method as claimed in claim 5, wherein the step of
identifying the correct operation of the electrical switching unit
also comprises: determining a first time at which the second
semiconductor switching element changes from the activated state
into the deactivated state, determining a second time at which the
voltage measured on the first semiconductor switching element falls
below the first supply voltage potential by the first threshold
value, and identifying the correct operation of the electrical
switching unit if the second time occurs within a predetermined
duration after the first time.
7. The method as claimed in claim 5, wherein the correct operation
of the electrical switching unit is identified only if the voltage
measured on the first semiconductor switching element falls below
the first supply voltage potential by the second threshold value
for a pre-defined second minimum duration.
8. The method as claimed in claim 5, further comprising: allowing a
re-activation of the second semiconductor switching element if the
correct operation of the electrical switching unit has been
identified.
9. A computer program product having at least one non-transitory
computer-readable memory medium with program code instructions
which are stored thereon and which are executable by a computer,
wherein the program code instructions which are executable by a
computer are configured to carry out a method as claimed in claim
1.
10. A full bridge circuit for operating an inductive load,
comprising: a first semiconductor switching element for supplying
the inductive load with a first supply voltage potential, a second
semiconductor switching element for powering the inductive load
with a second supply voltage potential, wherein the second supply
voltage potential has a lower value compared to the first supply
voltage potential and wherein the first semiconductor switching
element and the second semiconductor switching element each have a
diode, and a control device which is configured to carry out a
method as claimed in claim 1.
11. The method as claimed in claim 2, wherein the correct operation
of the electrical switching unit is only identified if the voltage
measured on the second semiconductor switching element falls below
the second supply voltage potential by the first threshold value
for a pre-defined first minimum duration.
12. The method as claimed in claim 6, wherein the correct operation
of the electrical switching unit is identified only if the voltage
measured on the first semiconductor switching element falls below
the first supply voltage potential by the second threshold value
for a pre-defined second minimum duration.
13. A computer program product having at least one non-transitory
computer-readable memory medium with program code instructions
which are stored thereon and which are executable by a computer,
wherein the program code instructions which are executable by a
computer are configured to carry out a method as claimed in claim
5.
14. A full bridge circuit for operating an inductive load,
comprising: a first semiconductor switching element for supplying
the inductive load with a first supply voltage potential, a second
semiconductor switching element for powering the inductive load
with a second supply voltage potential, wherein the second supply
voltage potential has a lower value compared to the first supply
voltage potential and wherein the first semiconductor switching
element and the second semiconductor switching element each have a
diode, and a control device which is configured to carry out a
method as claimed in claim 5.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to German Patent
Application No. 10 2018 220 861.1, filed Dec. 3, 2018, the contents
of such application being incorporated by reference herein.
FIELD OF THE INVENTION
[0002] The present invention relates to a method for identifying a
correct operation of an electrical switching unit, in particular an
electrical switching unit in a vehicle. The invention further
relates to a computer program product for executing such a method
and to a full bridge circuit having a control device for executing
such a method.
BACKGROUND OF THE INVENTION
[0003] Full bridge circuits are commonly arranged in an electrical
switching unit and are used, among other things, to operate an
inductive load, such as a motor or a solenoid valve.
[0004] To ensure that the electrical switching unit has not
incurred a fault or a short circuit, which may potentially damage
components of the electrical switching unit, it is necessary to
check the correct operation of the electrical switching unit.
[0005] However, it has been shown that checking the electrical
switching unit for correct operation is not always carried out with
the required reliability. Thus, it can happen that a fault or
short-circuit occurring in the electrical switching unit is not
detected as such.
SUMMARY OF THE INVENTION
[0006] An aspect of the present invention, therefore, is a method,
a computer program product and a full bridge circuit with which the
correct operation of an electrical switching unit can be more
reliably identified.
[0007] According to a first aspect of the present invention, a
method is provided for identifying a correct operation of an
electrical switching unit, which has a full bridge circuit and an
inductive load operated by means of the full bridge circuit. The
full bridge circuit comprises a first semiconductor switching
element for supplying the inductive load with a first supply
voltage potential and a second semiconductor switching element for
supplying the inductive load with a second supply voltage
potential, which has a smaller value compared to the first supply
voltage potential. Furthermore, the first semiconductor switching
element and the second semiconductor switching element each have a
diode, which can be provided in the form of a substrate diode or as
a separate component. The method according to an aspect of the
invention comprises the following steps: determining that the first
semiconductor switching element changes from an activated state
into a deactivated state, measuring a voltage applied to the second
semiconductor switching element, comparing the measured voltage
with a predefined first threshold value, and identifying that, if
the voltage measured on the second semiconductor switching element
falls below the second supply voltage potential by the predefined
first threshold value, the electrical switching unit is operating
correctly.
[0008] An aspect of the invention is based on the idea that the
correct operation of the electrical switching unit is not monitored
during the activated state of the first semiconductor switching
element, but during the deactivated phase of the second
semiconductor switching element, in particular during the passive
freewheeling phase of the second semiconductor switching element.
This has the advantage that the monitoring of the correct operation
can be carried out reliably even if the activated state of the
first semiconductor switching element or the safe
through-connection phase of the first semiconductor switching
element is comparatively short, thereby complicating a reliable
detection of the through-connection phase.
[0009] According to a particularly advantageous design of the
method according to an aspect of the invention, the step of
identifying the correct operation of an electrical switching unit
also comprises the following steps: determining a first time at
which the first semiconductor switching element changes from the
activated state into the deactivated state, determining a second
time at which the voltage measured on the second semiconductor
switching element falls below the second supply voltage potential
by the first threshold value, and identifying the correct operation
of the electrical switching unit if the second time occurs within a
predetermined duration after the first time. By determining the
first and second time, the correct operation of the electrical
switching unit can be identified simply and reliably. The
above-mentioned predetermined duration can be based on empirical
values or modelled values and is usually chosen in such a way that
the correct operation of the electrical switching unit is reliably
identified.
[0010] According to a further preferred embodiment, the correct
operation of the electrical switching unit is identified only when
the voltage measured on the second semiconductor switching element
falls below the second supply voltage potential by the first
threshold value for a pre-defined first minimum duration. The fact
that the measured voltage must undershoot the second supply voltage
potential by the first threshold value for a predefined first
minimum duration before the correct operation of the electrical
switching unit is identified ensures that minor fluctuations in the
measured voltage are not identified immediately as faults or the
absence of correct operation. This increases the robustness of the
method. The first minimum duration can be based on empirical or
modelled values and be adjusted to suit the respective
application.
[0011] According to a further preferred configuration, the method
also comprises the following step: allowing a re-activation of the
first semiconductor switching element if or once the correct
operation of the electrical switching unit has been identified.
This ensures that in the case of a correctly operating switching
unit the inductive load can continue to be operated correctly by
means of the full bridge circuit. However, if a fault were to occur
in the electrical control unit, i.e., the method were unable to
identify the correct operation of the electrical switching unit,
then a reactivation of the first semiconductor switching element
would not be allowed, in fact prevented. This ensures that in the
event of a non-functional switching unit, damage to the inductive
load or other components of the electrical switching unit is
prevented at the earliest possible stage.
[0012] According to a second aspect of the present invention, a
method is provided for identifying a correct operation of an
electrical switching unit, which has a full bridge circuit and an
inductive load operated by means of the full bridge circuit. The
full bridge circuit comprises a first semiconductor switching
element for supplying the inductive load with a first supply
voltage potential and a second semiconductor switching element for
supplying the inductive load with a second supply voltage
potential, which has a smaller value compared to the first supply
voltage potential. Furthermore, the first semiconductor switching
element and the second semiconductor switching element each have a
diode, which can be provided in the form of a substrate diode or as
a separate component. The method according to an aspect of the
invention comprises the following steps: determining that the
second semiconductor switching element changes from an activated
state into a deactivated state, measuring a voltage applied to the
first semiconductor switching element, comparing the measured
voltage with a predefined second threshold value and identifying
that, if the measured voltage on the first semiconductor switching
element falls below the first supply voltage potential by the
predefined second threshold value, the electrical switching unit is
operating correctly.
[0013] By means of the second aspect of the method according to the
invention, as is the case due to the first aspect of the method
according to the invention the correct operation of the electrical
switching unit is identified on the basis of the passive
freewheeling phase and not on the basis of the through-connection
phase of the respective semiconductor switch element. The method
according to the first aspect relates to the case that the first
semiconductor switching element changes from the activated state
into the deactivated state, wherein the correct operation of the
electrical switching unit is then checked on the basis of the
passive freewheeling phase of the second semiconductor switching
element. The method according to the second aspect, on the other
hand, relates to the converse case, whereby the second
semiconductor switching element changes from the activated state
into the deactivated state and the correct operation of the
electrical switching unit is identified based on the passive
freewheeling phase of the first semiconductor switching element. In
the same way as the method according to the first aspect, the
method according to the second aspect also has the advantage that
in the case of comparatively short through-connecting phases of the
second semiconductor switching element, the correct operation of
the electrical control unit can still be reliably identified.
[0014] According to a particularly preferred configuration of the
method according to the second aspect, the step of identifying the
correct operation of the electrical switching unit also has the
following steps: determining a first time at which the second
semiconductor switching element changes from the activated state
into the deactivated state, determining a second time at which the
voltage measured on the first semiconductor switching element falls
below the first supply voltage potential by the second threshold
value, and identifying the correct operation of the electrical
switching unit if the second time occurs within a predetermined
duration after the first time. In this configuration also, the
determination of the first and second times provides a means with
which the correct operation of the electrical switching unit can be
identified simply and reliably. The predefined duration can again
be based on empirical or modelled values.
[0015] According to a further preferred embodiment of the method
according to the secondary aspect, the correct operation of the
electrical switching unit is identified only if the voltage
measured on the first semiconductor switching element falls below
the first supply voltage potential by the second threshold value
for a pre-defined second minimum duration. The fact that the
measured voltage must exceed the first supply voltage potential by
the second threshold value for a predefined second minimum duration
before the correct operation of the electrical switching unit is
identified, ensures that minor fluctuations in the measured voltage
are not identified immediately as faults or the absence of correct
operation. As a result, as in the method in accordance with the
first aspect, the robustness of the method is increased. The second
minimum duration can, in turn, be based on empirical or modelled
values and be adapted to the respective application. The second
minimum duration may be the same as or different from the first
minimum duration.
[0016] According to a further preferred configuration, the method
also comprises the following step: allowing a re-activation of the
second semiconductor switching element if or once the correct
operation of the electrical switching unit has been identified.
This ensures that in the case of a correctly operating switching
unit the inductive load can continue to be operated correctly by
means of the full bridge circuit. However, if a fault were to occur
in the electrical control unit, i.e., the method were unable to
identify the correct operation of the electrical switching unit,
then a reactivation of the second semiconductor switching element
would not be allowed, in fact prevented. This ensures that in the
event of a non-functional switching unit, damage to the inductive
load or other components of the electrical switching unit is
prevented at the earliest possible stage.
[0017] According to a third aspect of the present invention, a
computer program product having at least one computer-readable
memory medium with program code instructions which are stored
thereon and which are executable by a computer is provided, wherein
the program code instructions which are executable by a computer
are configured to carry out a method according to the first aspect
and/or second aspect and embodiments thereof. The computer-readable
memory medium can be designed, for example, as a flash memory.
[0018] Finally, according to a fourth aspect of the present
invention a full bridge circuit to operate an inductive load is
provided. The full bridge circuit comprises a first semiconductor
switching element for supplying the inductive load with a first
supply voltage potential, and a second semiconductor switching
element for supplying the inductive load with a second supply
voltage potential, the second supply voltage potential having a
lower value compared to the first supply voltage potential and both
the first semiconductor switching element and the second
semiconductor switching element each having a diode in the form of
a substrate diode or a separate component. The full bridge circuit
also comprises a control device which is configured to execute a
method according to the first aspect and/or the second aspect, as
well as embodiments thereof.
[0019] Advantageous embodiments of the method according to aspects
of the invention can be considered to be advantageous embodiments
of the computer program product and of the full bridge circuit.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] Further features and aspects of the present invention will
become apparent to a person skilled in the art by practising the
present teaching and taking into consideration the accompanying
drawings. The drawings show:
[0021] FIG. 1 an electrical switching unit with a full bridge
circuit according to an aspect of the invention and an inductive
load,
[0022] FIG. 2 a schematic view of signal characteristics for a
switching sequence of a first and second semiconductor switching
element of the full bridge circuit of FIG. 1,
[0023] FIG. 3 a schematic view of a voltage characteristic of a
voltage applied to the second semiconductor switching element,
[0024] FIG. 4 a schematic view of a voltage characteristic of a
voltage applied to the first semiconductor switching element,
[0025] FIG. 5 an embodiment of a method according to the invention,
according to the first aspect,
[0026] FIG. 6 a further embodiment of the method according to the
invention, according to the first aspect,
[0027] FIG. 7 a further embodiment of the method according to the
invention, according to the first aspect,
[0028] FIG. 8 an embodiment of a method according to the invention,
according to the second aspect,
[0029] FIG. 9 a further embodiment of the method according to the
invention, according to the second aspect and
[0030] FIG. 10 a further embodiment of the method according to the
invention, according to the second aspect.
[0031] Elements of the same design or function are labelled with
the same reference symbols across all figures.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0032] Reference is made first to FIG. 1, which shows an electrical
switching unit 10 with a full bridge circuit 12 and an inductive
load 14. The full bridge circuit 12 has a first semiconductor
switching element M1 and a second semiconductor switching element
M2. The full bridge circuit 12 also has a first switch S1 and a
second switch S2, and an inductive load (represented by a coil L1
and a resistor R1) arranged between the bridge branches. The
inductive load 14 can be a motor and, in particular a motor for
driving an opening element such as a door or tailgate of a vehicle,
or can be a different inductive load such as a solenoid valve, for
example.
[0033] The first semiconductor switching element M1 is used to
supply the inductive load 14 with a first supply voltage potential
16 and the second semiconductor switching element M2 is used to
supply the inductive load 14 with a second supply voltage potential
18, the second supply voltage potential 18 having a lower value
compared to the first supply voltage potential 16. In the specific
example of FIG. 1 the first supply voltage potential is a supply
voltage VS, for example, and the second supply voltage potential 18
is ground (or earth) GND, for example.
[0034] The semiconductor switching elements M1, M2 switch an output
voltage OUT to either the supply voltage VS or to ground GND. The
direction of the current through the inductive load 14 is
determined by the switches S1, S2, as is known to the person
skilled in the art. In the specific example of FIG. 1 the inductive
load 14 is terminated to ground by the second switch S2.
[0035] As also shown in the specific example of FIG. 1, the first
semiconductor switching element M1 and the second semiconductor
switching element M2 are each implemented as metal oxide
semiconductor field-effect transistors (MOSFETs), which in turn
each have a substrate diode D1 or D2 and a transistor T1 or T2. In
other embodiments, the semiconductor switching elements M1, M2 can
also be implemented as bipolar transistors and the diodes D1, D2
can be implemented as separate components.
[0036] The electrical switching unit 10 also has a control device
20 for controlling the semiconductor switching elements M1, M2. The
control device 20 comprises a control and evaluation unit 22 and a
comparator COMP-H for the first semiconductor switching element M1
and a comparator COMP-L for the second semiconductor switching
element M2. The control unit 20 controls the semiconductor
switching elements M1, M2 so that the semiconductor switching
elements M1, M2 are never in the activated state at the same time,
or never conducting at the same time.
[0037] Reference is now made to FIG. 2, which shows a schematic
view of signal characteristics for a switching sequence of the
first and second semiconductor switching elements M1, M2 of the
full bridge circuit 12 of FIG. 1.
[0038] Specifically, FIG. 2 shows the control signal G1 for the
first semiconductor switching element M1 and the control signal G2
for the second semiconductor switching element M2. During the time
interval t_CCP the two control signals G1, G2 are set to LOW, which
means that during this time both semiconductor switching elements
M1, M2 are turned off or in the deactivated state.
[0039] If current now already flows through the inductive load 14,
in the phase in which the two semiconductor switching elements M1,
M2 are turned off the current continues to flow through the
substrate diodes D1, D2. Since in this specific example the
inductive load 14 is terminated to ground (second switch S2 is in
the closed state), in the phase in which both semiconductor
switching elements M1, M2 are turned off, a current flows through
the substrate diode D2 of the second semiconductor switching
element M2. In this so-called passive freewheeling phase the output
voltage OUT thus falls below the second supply voltage potential
18, that is to say, in the specific case below GND. This is shown
schematically in FIG. 2 by the "hump" 24.
[0040] If the first semiconductor switching element M1 now switches
from the deactivated state into the activated state, for example by
the control signal G1 switching to HIGH, the output voltage OUT
rises to the value VS. As a result of system-related processes,
however, the output voltage OUT does not change instantaneously
from GND to VS. Instead, it takes a certain time until the output
voltage OUT reaches the value VS, as is known to the person skilled
in the art. Not until the output voltage OUT has reached the value
VS is it possible to speak of a safe "through-connection" of the
first semiconductor switching element M1. The phase of the safe
through connection of the first semiconductor switching element M1
is marked schematically by the arrow 26.
[0041] If the first semiconductor switching element M1 is now
turned off again by the control signal G1 switching to LOW,
essentially the already described passive freewheeling occurs at
the second semiconductor switching element M2 (represented by the
"hump" 27), so that the output voltage OUT falls to a value below
GND again.
[0042] If in the deactivated state of the first semiconductor
switching element M1 the second semiconductor switching element M2
switches from the deactivated state into the activated state (for
example, by the control signal G2 switching to HIGH), the output
voltage OUT rises to the value GND. Due to the system-related
processes described, it again takes a certain time until the output
voltage OUT reaches the value GND. Not until the output voltage OUT
has reached the value GND, is it again possible to speak of a safe
"through connection" of the second semiconductor switching element
M2. The phase of the safe through connection of the second
semiconductor switching element M2 is marked schematically by the
arrow 28.
[0043] If the second semiconductor switching element M2 is then
turned off, for example by the control signal G2 switching to LOW,
and in this switching phase the coil L1 still has energy stored in
the magnetic field, the output voltage OUT again falls to a value
below GND. The consequence of this is that even in this switching
phase a "hump" (represented by the arrow 30) occurs.
[0044] To determine the correct operation of the electrical
switching unit 10, in the prior art up to now a voltage drop across
the semiconductor switching elements M1, M2 during the safe
through-connection phases 26, 28 has been used. However, it has
been shown that it is not always possible to determine the safe
through-connection phases 26, 28 correctly, depending on the
particular application. In particular, if the on phases of the
semiconductor switching elements M1, M2 become very short, for
example due to a pulse-width modulated control of the inductive
load 14, the safe through-connection phase 26, 28 can become so
short that it essentially vanishes. If a short circuit were to
occur in this case, with the methods used in the prior art up to
now this would not be detectable or identifiable.
[0045] Referring now to FIG. 3, this shows a schematic view of a
voltage characteristic of a voltage 40 applied to the second
semiconductor switching element M2.
[0046] As already mentioned in connection with FIG. 2, in the case
in which the first semiconductor switching element M1 switches from
the activated state into the deactivated state the voltage 40
applied to the second semiconductor switching element M2 falls to a
value below GND. This is shown by the "humps" 32-38.
[0047] The idea of an aspect of the present invention then involves
identifying the correct operation of the electrical switching unit
10 not on the basis of the through-connection phases of the first
semiconductor switching element M1, but instead on the basis of the
"humps" 32-38, which means on the basis of the passive freewheeling
of the second semiconductor switching element M2.
[0048] In concrete terms, the correct operation may be identified
by the fact that the voltage 40 measured on the second
semiconductor switching element M2 falls below a value of GND by a
predefined first threshold value 42. As long as the measured
voltage 40 is below GND by the first threshold 42, it can be
assumed that the electrical switching unit 10 is fully operational.
If the measured voltage 40 were not to fall below GND by the first
threshold 42, then it would no longer be possible to assume the
correct operation of the electrical switching unit and a fault or
short circuit in the electrical switching unit 10 would have to be
assumed. Because the passive freewheeling ("humps" 32-38) also
occurs when the safe through-connection phase of the first
semiconductor switching element M1 is very short, or in some cases
even "disappears", then even for very short through-connection
phases of the first semiconductor switching element M1 the correct
operation of the electrical switching unit 10 can be reliably
identified.
[0049] The correct operation of the electrical switching unit 10
can be identified, for example, by the fact that a first time t1 is
identified, at which the first semiconductor switching element M1
changes from the activated state into the deactivated state.
Furthermore, a second time t2 can be determined, at which the
measured voltage 40 is below GND by the first threshold 42. If the
second time occurs within a predetermined duration .DELTA.t after
the first time, it can be assumed that the electrical switching
unit 10 is operating correctly. The predetermined duration .DELTA.t
or the temporal interval between the first time t1 and the second
time t2 can be estimated, for example, from empirical or modelled
values.
[0050] In order to make the method more robust, a first minimum
period 44 can also be introduced, for which the measured voltage 40
must remain below GND by the first threshold value 42 before a
correct operation of the electrical switching unit 10 is assumed.
The first minimum duration 44 allows even minor fluctuations of the
measured voltage 40 not to be immediately evaluated as faults in
the electrical switching unit 10. The first minimum duration 44 can
again be based on empirical or modelled values.
[0051] As also shown in FIG. 3, during the subsequent switching
cycle of the first semiconductor switching element M1 or after the
repeated deactivation of the first semiconductor switching element
M1 the passive freewheeling of the second semiconductor switching
element M2 occurs again. Even if in this passive freewheeling phase
the electrical switching unit 10 is correctly operational, the
measured voltage 40 on the second semiconductor switching element
M2 then falls again to a value which is below GND by the first
threshold value 42. A third time t3 can therefore be determined, at
which in the following switching cycle or after a subsequent
repeated deactivation of the first semiconductor switching element
M1 the measured voltage 40 falls below GND by the first threshold
value 42. If the third time t3 now occurs within a predetermined
duration .DELTA.t2 after the second time t2, it can be assumed that
the electrical switching unit 10 is operating correctly. This
variant of the detection of the correct operation of the electrical
switching unit 10 is particularly advantageous when the inductive
load 14 is activated by means of a pulse-width modulated signal. In
that case the predetermined duration .DELTA.t2 can then be selected
as a function of a duration of the period of the pulse-width
modulated signal. If the third time t3 does not occur within a
period-duration dependent time interval (for example, period
duration*110%) after the second time t2, it can be assumed that the
electrical switching unit 10 is no longer functioning correctly and
instead, a fault or short circuit has occurred in the electrical
switching unit 10.
[0052] The times t1, t2 and t3 can be provided by means of a
trigger signal, so that the calculation of the durations .DELTA.t1
and .DELTA.t2 requires little computational effort.
[0053] Referring now to FIG. 4, this shows a schematic view of a
voltage characteristic of a voltage 46 applied to the first
semiconductor switching element M1.
[0054] As can be seen, in the case of a change of the second
semiconductor switching element M2 from the activated state into
the deactivated state the voltage 46 applied to the first
semiconductor switching element M1 rises to a value above VS.
Again, this is shown by the "humps" 48-54.
[0055] The idea of an aspect of the present invention then is that
even in such a case the correct operation of the electrical
switching unit 10 is not identified on the basis of the safe
through-connection phases of the second semiconductor switching
element M2, but on the basis of the "humps" 48-54, that is to say,
on the basis of the passive freewheeling of the first semiconductor
switching element M1.
[0056] In concrete terms, the correct operation can be identified
by the fact that the voltage 46 measured on the first semiconductor
switching element M1 exceeds a value of VS by a predefined second
threshold value 56. As long as the measured voltage 46 is above VS
by the second threshold value 56, it can be assumed that the
electrical switching unit 10 is fully operational. If the measured
voltage 46 were not above VS by the second threshold 56, then the
correct operation of the electrical switching unit 10 can no longer
be assumed and a fault or short circuit in the electrical switching
unit 10 would have to be assumed. Because the passive freewheeling
("humps" 48-54) also occurs when the safe through-connection phase
of the second semiconductor switching element M2 is very short, or
in some cases even "disappears", then even for very short
through-connection phases of the second semiconductor switching
element M2 the correct operation of the electrical switching unit
10 can be reliably identified.
[0057] The correct operation of the electrical switching unit 10
can be identified, for example, by the fact that a first time t1 is
again identified, at which the second semiconductor switching
element M2 changes from the activated state into the deactivated
state. Furthermore, a second time t2 can be determined, at which
the measured voltage 46 is above VS by the second threshold 56. If
the second time occurs within a predetermined duration .DELTA.t
after the first time, it can be assumed that the electrical
switching unit 10 is operating correctly. The predetermined
duration .DELTA.t or the temporal interval between the first time
t1 and the second time t2 can again be estimated, for example,
using empirical or modelled values.
[0058] In order to make the method more robust, a second minimum
period 58 can also be introduced, for which the measured voltage 46
must remain above VS by the second threshold value 56 before a
correct operation of the electrical switching unit 10 can be
assumed. Like the first minimum duration 44, the second minimum
duration 58 also allows minor fluctuations of the measured voltage
46 not to be immediately evaluated as faults in the electrical
switching unit 10. The second minimum duration 58 can also be based
on empirical or modelled values.
[0059] As also shown in FIG. 4, during the subsequent switching
cycle of the second semiconductor switching element M2 or after the
repeated deactivation of the first semiconductor switching element
M2, the passive freewheeling of the first semiconductor switching
element M1 occurs again. Even if in this passive freewheeling phase
the electrical switching unit 10 is correctly operational, the
measured voltage 46 on the first semiconductor switching element M1
then rises to a value which is above VS by the second threshold
value 56. A third time t3 can therefore be determined, at which in
the following switching cycle or after a subsequent repeated
deactivation of the second semiconductor switching element M2 the
measured voltage 46 is above VS by the second threshold value 56.
If the third time t3 now occurs within a predetermined duration
.DELTA.t2 after the second time t2, it can be assumed that the
electrical switching unit 10 is operating correctly. As in the case
of FIG. 3 also, this variant of the identification of the correct
operation of the electrical switching unit 10 is particularly
advantageous when the inductive load 14 is activated by means of a
pulse-width modulated signal. The predetermined duration .DELTA.t2
can then be selected as a function of a duration of the period of
the pulse-width modulated signal. If the third time t3 does not
occur within a period-duration dependent time interval (for
example, period duration*110%) after the second time t2, it can be
assumed that the electrical switching unit 10 is no longer
functioning correctly and instead, a fault has occurred in the
electrical switching unit 10.
[0060] The times t1, t2 and t3, as in the case of FIG. 3, can be
provided by means of a trigger signal, so that the calculation of
the durations .DELTA.t1 and .DELTA.t2 requires little computational
effort.
[0061] Reference is now made to FIG. 5, which shows an embodiment
of a method according to an aspect of the invention. In the method
described under FIG. 5, the correct operation of the electrical
switching unit 10 is identified on the basis of the passive
freewheeling phase of the second semiconductor switching device M2.
The method according to FIG. 5 therefore takes into account a
voltage characteristic, such as that shown in FIG. 3, for example.
In the following the individual steps of the method are described
in detail in connection with FIGS. 1 to 3.
[0062] The method begins with the start at step 500. In the
subsequent step 502 it is determined that the first semiconductor
switching element M1 changes from an activated state into a
deactivated state. In the following step 504 a voltage applied to
the second semiconductor switching element M2 (for example, voltage
40 of FIG. 3) is determined. In the following step 506, the
measured voltage 40 is compared with a predefined first threshold
(for example, threshold 42 of FIG. 3). The comparison is carried
out, for example, with the comparator COMP-L (see FIG. 1). In the
following step 508, the correct operation of the electrical
switching unit 10 is then identified if the measured voltage 40 is
below the second supply voltage potential 18 by the first threshold
42 (in the specific example GND).
[0063] If in step 508 the correct operation of the electrical
switching unit 10 were identified, then in a step 510 the repeated
activation of the first semiconductor switching element M1 would be
allowed, so that the method jumps back again to step 502, in which
it is determined once again whether the first semiconductor
switching element M1 in turn changes from the activated state into
the deactivated state. In the event that the first semiconductor
switching element M1 changes once again into the deactivated state,
the previously described steps 504 to 508 are executed again until
the correct operation of the electrical switching unit 10 is no
longer identified. In this case, the method jumps back to step 512,
in which the method detects or outputs a fault and/or
terminates.
[0064] Reference is now made to FIG. 6 which shows an embodiment of
the method of FIG. 5. The method in accordance with FIG. 6 like the
method according to FIG. 5 also has the steps 500 to 512. In
contrast to the method of FIG. 5, however, in the method of FIG. 6
the correct operation (step 508) is identified by means of the
following steps. First, in a step 600 a first time (for example,
time t1 of FIG. 3) is determined, at which the first semiconductor
switching element M1 changes from the activated state into the
deactivated state. Then, in step 602, a second time (for example,
time t2 of FIG. 3) is determined at which the measured voltage 40
falls below the second supply voltage potential 18 (in the specific
example, GND) by the first threshold value 42. Then, in step 604
the correct operation of the electrical switching unit 10 is
identified if the second time t2 occurs within a predetermined
duration (for example duration .DELTA.t of FIG. 3) after the first
time t1. In this embodiment, the correct operation of the
electrical switching unit 10 can be identified or detected by a
simple temporal comparison of two times t1, t2. If the second time
t2 were then to occur within the duration .DELTA.t after the first
time t1, then the method would confirm the correct operation of the
electrical switching unit 10 and jump to step 510. In the other
case, the method would jump to step 512.
[0065] Reference is now made to FIG. 7 which shows another
embodiment of the method according to FIG. 5. The method according
to FIG. 7 again comprises the steps 500 to 506, and the steps 510
and 512. In the method according to FIG. 7, however, in a step 700
the correct operation is detected not only based on the fact that
the measured voltage 40 falls below the second supply voltage
potential 18 (in the specific example, GND) by the first threshold
value 42. But it must also be ensured that the measured voltage 40
falls below the second supply voltage potential 18 by the first
threshold value 42 for a predetermined first minimum duration (for
example, minimum duration 44 of FIG. 3). As mentioned, the minimum
duration 44 increases the robustness of the method.
[0066] If in step 700 the correct operation is then identified, the
method then jumps to step 510. In the other case, the method jumps
to step 512, in which a fault is detected and/or output, or the
method is terminated.
[0067] Of course it is possible to combine the embodiments of the
method according to FIGS. 5 to 7 in any desired way.
[0068] Reference is now made to FIG. 8, which shows another
embodiment of a method according to an aspect of the invention. In
contrast to the methods referred to in FIGS. 5 to 7, in the method
according to FIG. 8 the correct operation of the electrical
switching unit 10 is identified on the basis of the passive
freewheeling phase of the first semiconductor switching element M1.
The method according to FIG. 8 therefore takes into account a
voltage characteristic, such as that shown in FIG. 4, for example.
In the following the individual steps of the method are described
in detail in connection with FIGS. 1 to 2 and 4.
[0069] The method begins with the start at step 800. In the
subsequent step 802 it is determined that the second semiconductor
switching element M2 changes from an activated state into a
deactivated state. In the following step 804 a voltage applied to
the first semiconductor switching element M1 (for example, voltage
46 of FIG. 4) is determined. In the following step 806, the
measured voltage 46 is compared with a predefined second threshold
value (for example, threshold 56 of FIG. 4). The comparison is
carried out, for example, with the comparator COMP-H (see FIG. 1).
In the following step 808, the correct operation of the electrical
switching unit 10 is identified if the measured voltage 46 is above
the first supply voltage potential 16 by the second threshold value
56 (in the specific example VS).
[0070] If in step 808 the correct operation of the electrical
switching unit 10 were identified, then in a step 810 the repeated
activation of the second semiconductor switching element M2 would
be allowed, so that the method jumps back to step 802, in which it
is determined once again whether the second semiconductor switching
element M2 in turn changes from the activated state into the
deactivated state. In the event that the second semiconductor
switching element M2 changes once again into the deactivated state,
the previously described steps 804 to 808 are executed again until
the correct operation of the electrical switching unit 10 is no
longer identified. In this case, the method jumps back to step 812,
in which the method detects or outputs a fault and/or
terminates.
[0071] Reference is now made to FIG. 9 which shows an embodiment of
the method of FIG. 8. The method in accordance with FIG. 9 like the
method according to FIG. 8 also has the steps 800 to 812. In
contrast to the method of FIG. 8, however, in the method of FIG. 9
the correct operation (step 808) is identified by means of the
following steps. First, in a step 900 a first time (for example,
time t1 of FIG. 4) is determined, at which the second semiconductor
switching element M2 changes from the activated state into the
deactivated state. Then, in step 902, a second time (for example,
time t2 of FIG. 4) is determined at which the measured voltage 46
exceeds the first supply voltage potential 16 (in the specific
example, VS) by the second threshold value 56. Then, in step 904
the correct operation of the electrical switching unit 10 is
identified if the second time t2 occurs within a predefined
duration (for example duration .DELTA.t of FIG. 4) after the first
time t1. In this embodiment, the correct operation of the
electrical switching unit 10 can be identified or detected by a
simple temporal comparison of two times t1, t2. If the second time
t2 were then to occur within the duration .DELTA.t after the first
time t1, then the method would confirm the correct operation of the
electrical switching unit 10 and jump to step 810. In the other
case, the method would jump to step 812.
[0072] Reference is now made to FIG. 10 which shows another
embodiment of the method according to FIG. 8. The exemplary
embodiment according to FIG. 10 again comprises the steps 800 to
806, and the steps 810 and 812. In the method according to FIG. 10,
however, in a step 1000 the correct operation is identified not
only based on the fact that the measured voltage 46 exceeds the
first supply voltage potential 16 (in the specific example, VS) by
the second threshold value 56. But it must also be ensured that the
measured voltage 46 exceeds the first supply voltage potential 16
by the second threshold value 56 for a predetermined second minimum
duration (for example, minimum duration 58 of FIG. 4). As
mentioned, the minimum duration 58 increases the robustness of the
method.
[0073] If in step 1000 the correct operation is then identified,
the method then jumps to step 810. In the other case, the method
jumps to step 812, in which a fault is detected and/or output, or
the method is terminated.
[0074] Of course it is possible to combine the embodiments of the
method according to FIGS. 8 to 10 in any desired way.
[0075] It is also possible to combine the methods referred to in
FIGS. 5 to 7 with the methods referred to in FIGS. 8 to 10 in an
appropriate manner, so that the corresponding method (in accordance
with FIGS. 5 to 7 or in accordance with FIGS. 8 to 10) is always
applied when the corresponding first or second semiconductor
switching element M1, M2 changes from the activated state to the
deactivated state.
[0076] The control device 20 is designed to carry out the steps of
the methods according to FIGS. 5 to 10. The methods according to
FIGS. 5 to 10 can be implemented, for example, as a computer
program product on the control device 20.
[0077] In addition, the methods disclosed here in connection with
FIGS. 5 to 10 can be combined with the methods known from the prior
art to identify the correct functioning of the electrical switching
unit 10. For example, in sufficiently long switched-on phases of
the semiconductor switching elements M1, M2, the correct operation
could be identified on the basis of the monitoring of the safe
through-connection phase known from the prior art, and in
relatively short switched-on phases the correct operation could be
identified on the basis of the methods according to aspects of the
invention, that is on the basis of the monitoring of the passive
freewheeling phase. It is also possible according to an aspect of
the invention to provide the monitoring of the passive freewheeling
phase as an additional safeguard for monitoring the safe
through-connection phase, in particular in comparatively short
switched-on phases of the semiconductor switching elements M1,
M2.
* * * * *